Finely particulated colloidal platinum compound and sol for producing the same and method of preparation of fuel cell electrodes and the like employing the same

ABSTRACT

This disclosure deals with novel very fine, particulated colloidal platinum of the 15-25 Angstrom size range of unusual catalytic activity and particularly adapted for adsorption or other deposition upon carbon for use as fuel cell catalytic electrodes and the like and produced from platinum colloids and sols including complex platinum sulfite compounds and sols derived therefrom.

.Iadd.This application for reissue is a continuation of ReissueApplication Ser. No. 007,626, filed Jan. 29, 1979, abandoned, for theReissue of Pat. No. 4,044,193, granted Aug. 23, 1977, based on Ser. No.535,731, filed Dec. 20, 1974; which is a continuation-in-part of Ser.No. 153,824, filed Jun. 16, 1971, abandoned; and which is a continuationof Ser. No. 430,190, filed Dec. 28, 1973, abandoned; Application Ser.No. 534,731 having been filed in response to a Patent Office requirementfor restriction or division in connection with catalytic fuel cellelectrodes and preparation methods thereof and the like, withsupplemental material. .Iaddend.

The present invention relates to a new platinum compounds, sols and aparticulated platinum deposits derived therefrom and to methods ofpreparing the same, being specifically, though not exclusively,concerned with use in fuel cell electrode preparation and the like.

The art is, of course, replete with numerous compounds and processesemployed to provide platinum deposits for use as catalysts in a myriadof applications including oxidation, hydrogenation, dehydrogenation,reforming, cracking, chemical reaction-aiding, contaminant burning,electrochemical cell electrode operation the like, all hereinaftergenerically connoted by reference to "catalytic" usage. Particulatedplatinum has been employed to provide increased effective surface area,as by adherence to rough substrata, such as carbon, alumina and othersubstances, such deposits being obtained from compounds such as platinumtetrachloride, chloroplatinic acid and the like. As described, forexample in Acted Du Deuxieme Congress International De Catalyse, Paris,1960, pp. 2236, 2237, the average particle size of such particulatedplatinum lies in the range of from about 45 to 250 Angstroms, and it hasnot proven possible commercially to provide much smaller particles andthus obtain vastly increased catalytic efficiency.

In accordance with discoveries underlying the present invention,however, it has, in summary, now been found possible consistently toproduce excellently adhering particulated platinum deposits in the muchfiner 15-25 Angstrom range; and it is to new methods, compounds and solsfor producing the same that the present invention is accordinglyprimarily directed.

A further object of the invention is to provide a novel complex platinumacid compound and colloidal sol of more general application, as well.

Still another object is to provide novel catalytic structures to whichsuch finely deposited platinum particles are adsorbed and adhered.

The present application is particularly directed to catalytic fuel cellelectrodes and the like and methods of preparing the same that use oremploy derivatives of such novel complex platinum compounds and thelike.

Other and further objects will be explained hereinafter and are moreparticularly delineated in the appended claims.

A first discovery underlying a part of the invention resides in therather unexpected fact that a novel complex platinum sulphite acid voidof chlorine may be prepared from chloroplatinic acid and particularlyadapted for the formation of a colloidal sol from which extremely finelyparticulated platinum may be deposited. While prior experience had ledthose skilled in the art to consider either that adding SO₂ tochloroplatinic acid would invariably result in reducing the platinum tothe "2" state, without replacing chloride in the complex with SO₃ --,yielding chloroplatinous acid (see for example, H, Remy, Treatise onInorganic Chemistry, Vol. 2, p. 348), or that the reaction of SO₂ with aplatinum compound resulted in its reduction to the metallic or zerovalence state ("Applied Colloidal Chemistry", W. N. Bankcroft, McGrawHill, 1926, p. 54), it has been discovered that through appropriate pHand other controls, a complex platinum acid containing sulphite (and tothe complete exclusion of chloride) is decidedly achievable. And fromsuch complex acid, unusual colloidal sols depositing particulateplatinum in the 15-25 Angstrom range can readily be obtained, and thusvastly superior catalytic performance attained.

Specifically, one of the preferred methods for the preparation of thisnovel complex platinum acid (represented substantially by a formulacontaining two moles of SO₃ -- per mold of platinum) involves theneutralizing of chloroplatinic acid with sodium carbonate, formingorange-red Na₂ Pt (Cl)₆. Sodium bisulfite is then added, dropping the pHto about 4, and with the solution changing to pale yellow and then to asubstantially colorless shade. Adding more sodium carbonate brings thepH back to neutral (7), and a white precipitate forms in which theplatinum has been found to be contained in excess of 99% of the platinumcontained in the chloroplatinic acid starting sample. It was believed(now confirmed) that this precipitate contains six atoms of sodium andfour moles of SO₃ -- per atom of platinum. It is slurried with water,and then enough strong acid resin is added (such as sulfonated styrenedivinyl benzene in the hydrogen form--DOWEX-50, for example), to replacethereof the Na atoms. The solution is filtered to remove resin and thenpassed through an ion-exchange column with sufficient of the said acidresin to replace the other three Na atoms. Inherently, during thistwo-step cation exchange, copious quantities of SO₂ are liberated,amounting to a loss of substantially two moles of SO₂ /mole Pt. Boilingto concentrate the solution, results in the novel complex sulfiteplatinum acid compound above discussed containing groups of (OH) and H₃Pt (SO₃)₂, free of excess unbound SO₂.

In compliance with a requirement in the earlier applications from whichthe present application is continued, for evidence of the reasons forthe conclusion as to the above formulations, a summary of such evidenceis herein presented, though it is not in any way part of the essentialdisclosure of this application and is not required for the practice ofthe invention as originally disclosed, since precisely following thesteps of the disclosure of said applications will produce the preciseproducts and results of the invention as originally described.

Proof of the above-stated complex character of this novel platinum acidhas been obtained by reacting 0.0740 g-mole of chloroplatinic acid inthe form of the commercial material containing 40% by weight of Pt toform the "white precipitate" precisely in accordance with the methoddescribed above and in the said prior applications. The "whiteprecipitate" weighed 48.33 g, after filtering, washing and drying at150° C. (to constant weight). The filtrate contained 40 ppm platinum, asdetermined by atomic adsorption, showing that more than 99% of theoriginal platinum contained in the sample of chloroplatinic acid waspresent in the precipitate. Thus, the precipitate has an empiricalformula weight of about 653 based on one atom of Pt [48.33/0.0740]≃653.Chemical analysis showed that the salt contained 21% Na(by atomicadsorption), 29.9% Pt (by atomic adsorption) and 48.7% SO₃ (by oxidativefusion and BaSO₄ l precipitation and by KMnO₄ titration), therebyconfirming the presence of substantially 6 Na and 4 SO₃ per Pt atom.

The precipitate was then converted to the complex acid solution inaccordance with the precise procedure described above and in said priorapplications. It was boiled to a concentration approximately 2 molar inPt (2 g atoms Pt/liter of solution).

When the acid was concentrated to this strength, SO₂ was not longerevolved.

1. A sample of substantially water-free complex platinum acid, preparedby distillation under high vacuum, was found to contain 52% Pt by weightdetermined by thermogravimetric analysis.

2. A sample of complex platinum acid (in solution) was found to have asulfur content of 42% by weight, as SO₃, determined by oxidative fusionand BaSO₄ precipitation and by oxidometric titration with KMnO₄, i.e. 2moles of sulfite/mole Pt.

3. Titration of a sample of the complex platinum acid with standard baseshowed a characteristic titration curve with three titratable hydrogenions per atom of Pt, amounting to 0.8% by weight, two of which werestrongly acid (i.e. completely dissociated) and the third quite weaklyacid (K_(a)˜ 10⁻⁸ for the third H+ion).

4. A sample of complex platinum acid was found to contain one OH groupper atom Pt, or 4.54% by weight OH, determined by neutralizing the threeacid hydrogens with NaOH to pH 9.5, then reacting with excess sodiumsulphite solution of natural pH=9.5, thereby gradually reforming whiteprecipitate having the above described composition, and raising the pHof the reaction mixture above 12, and back-titrating with H₂ SO₄ to pH9.5.

5. A sample decomposed at about 400° C. in nitrogen yielded only oxidesof sulfur (SO₂ and SO₃) and water in the gas phase, and Pt metalresidue.

6. Addition of silver nitrate to the acid yielded a yellow productinsoluble in dilute sulfuric acid.

From these experiments, the following is concluded:

1. The acid contains only H, O, Pt and S. (The replacement of Na⁺ by H⁺in the ion exchange step cannot introduce any other element); Cl isabsent.

2. The acid contains Pt and S in the ratio of 1:2.

3. The sulfur is present as sulfite as shown by the analysis and by thehigh temperature decomposition of the acid in nitrogen.

4. The sulfite has to be complexed because (a) the complex acid (no SO₂odor) is completely dissociated whereas the ionization constants of H₂SO₃ (which is odorous) are 1.54×10⁻² and 1.02×10⁻⁷, respectively; (b)the complex acid is more soluble in water than H₂ SO₃ at the boilingpoint (max. solubility of SO₂ is 5.8 g/l or 0.07 molar in H₂ SO₃ ate100° C. vs. the 2 molar acid produced by the method of this invention);and (c) silver sulfite is soluble in dilute sulfuric acid, whereas thesilver salt of the new complex platinum acid is insoluble in dilutesulfuric acid.

5. The acid is trivalent, having two strongly acidic and a third weaklyacidic hydrogen as evidenced by a characteristic titration curve. Anunusual kinetic effect occuring during titration of the third hydrogensuggests the possibility that it could be part of the sulfite ligand.

Turning back, now, to the said "white precipitate", and in view of thePatent Office requirement promulgated since the filing of the saidearlier applications for disclosure of all known pertinent prior art,attention is invited to "The Chemistry of the Co-ordination Compounds",edited by John C. Bailer Jr., ACS Monograph, Reinhold Publishing Co.1956, pp. 57-58, where a compound of composition Na₆ Pt (SO₃)₄ isdisclosed (with no reference to any utility), but as having to beprepared by the complicated process of making the appropriate isomer ofa platinum ammine chloride, Pt (NH₃)₂ Cl₂, and then converting it to NaPt (SO₃)₄. This further points up the highly novel and greatlysimplified high-yield technique of the present invention, starting withchloroplatinic acid and preparing the sodium platinum sulfite complex"white precipitate" for which the present invention has found and taughtimportant utility in the development of the novel complex platinum acidof the invention), substantially quantitatively.

From this novel complex platinum acid, a new colloidal sol may beprepared by decomposing the acid by heating it to dryness in air(oxidizing) and holding the temperature at about 135° C. for about anhour, producing a black, glassy material which, when dispersed in water,yields a novel colloidal platinum-containing sol having an averagefinely divided platinum particle size of from about 15-25 Angstroms,with substantially all the platinum particles consistently lying withinthis range. Some platinum metal and sulfuric acid may be present and maybe respectively removed by filtering (and re-cycling use of the metallicplatinum) and by treating with hydroxide resin such as DOWEX 2 or thelike. A jet black colloidal sol with these fine size particles is thusobtained.

From this novel product, a host of vastly improved catalytic surfaceshave been obtained.

As a first example the sol has been deposited or adsorbed on a carbonblack substrata (such as electrically conductive Norit A) to form acatalytic electrode structure (by means well known in the art andcomprising a conventional current collector). One of the uses of such anelectrode structure for example, is as a cathode electrode in fuel cellsand the like. This has been effected by reducing the adsorbed metal ofthe sol with hydrazine; forming on the carbon, platinum metal crystalsof measured approximately 20-Angstrom size. For use as an oxygen cathodeelectrode in an air-hydrogen 135° C. fuel cell with phosphoric acidelectrolyte and a platinum anode, with both electrode sizes about 1 inchby 1 inch, about 2-10% by weight of adsorbed platinum was so reducedwith about 10% solution of hydrazine to form and adhere the fineparticulate platinum on the electrically conductive carbon stubstrate,the electrode structure exclusive of conventional components being about70% by weight of Norit A carbon and 30% by weight of Teflon (i.e. atypical fluorinated hydrocarbon polymer) emulsion, such as TFE 30. Mostremarkable cathode performance was obtained in this fuel cell, withcathode loading of only 0.25 milligrams/cm.² of platinum, as follows:

    ______________________________________                                        Current               Voltage                                                 amperes/ft..sup.2     millivolts                                              ______________________________________                                        100                   660                                                     200                   598                                                     300                   548                                                     400                   500                                                     ______________________________________                                    

This improved performance is evident from the fact that in anidentically operating cell with the cathode formed by adhering to thecarbon substrate platinum particles from platinum black of nominalsurface area of 25 meters ² /gram, such cell performance could only beobtained with ten times the platinum loading (i.e. 2 milligrams/cm.²).Similar performance could also be obtained in the same cell with theplatinum deposited on the carbon from platinum tetrachloride andchloroplatinic acid (approximately 40-80 Angstrom particles), but onlywith three to four times the platinum loading. Prior phosphoric acidfuel cell operation with other platinum catalysts is described, forexample, by W. T. Grubb et al., J. Electrochemical Society III, 1015,1964, "A High Performance Propane Fuel Cell Operating in the TemperatureRange of 150°-200° C.". Prior methods of fabricating fuel cellelectrodes are described, for example, in U.S. Pat. No. 3,388,004.

As another example, similar electrochemical cell electrodes wereoperated as air cathodes in the same cell as the first example with aslittle as 0.04 milligrams/cm.² platinum loading, and with as much as0.05 milligrams/cm.². The respective cell performance characteristicswere 100 amperes/ft.,² at 530 millivolts, and 100 amperes/ft.² at 690millivolts.

The above-described catalytic electrode structures have otheradvantages, for example when used as hydrogen anode electrodes in fuelcells and the like. As an illustration, the electrode structuredescribed above as a first example, was used as novel hydrogen anodeelectrode in the above mentioned air-hydrogen fuel cell in lieu of the(conventional) platinum anode also above mentioned. Remarkable anodeperformance was obtained in this fuel cell with low loadings between0.05 and 0.25 milligrams of platinum per cm² of anode area, particularlywith respect to improved tolerance of carbon monoxide. One knowncommercial method of producing low-cost hydrogen is by steam reformingof hydrocarbons followed by the shift reaction, which process yields animpure hydrogen containing typically of the order of 80% hydrogen, theremainder being CO₂, excess steam and of the order of 1%-2% carbonmonoxide. It is well known in the fuel cell art that carbon monoxide isa poison for anodic platinum and that such poisoning is temperaturedependent, the loss of anode performance being the more drastic, thelower the temperature. Using such low cost hydrogen, it is thusgenerally advantageous to operate the above phosphoric acid fuel cell athigher temperatures, for example in the range of 170° to 190° C.Remarkable anode performance in the presence of CO impurity, wasobtained in this fuel cell, especially at high current densities, withan anode loading of 0.05 milligrams/cm² of platinum when compared to theperformance of an anode having a conventional platinum catalyst(prepared by reaction of chloroplatinic acid and deposited insubstantially the same manner) and having the same loading of 0.05milligrams/cm², as shown in the following table.

    ______________________________________                                                         Loss of Voltage (millivolts)                                                  by Polarization Due to 1.6%                                  Cell     Current       CO in Hydrogen                                         Temper-  Density       Novel   Conventional                                   ature    (Amps/sq ft)  Anode   Anode                                          ______________________________________                                        190° C.                                                                         500           17      44                                             190° C.                                                                         400           10      28                                             190° C.                                                                         300            9      14                                             175° C.                                                                         500           66      118                                            175° C.                                                                         400           40      69                                             175° C.                                                                         300           22      38                                             ______________________________________                                    

In connection with the examples above, moreover, not only has greatlyimproved catalytic efficiency been obtained as a result of the extremelyhigh surface area provided by such fine colloidal particles, but thisenhanced activity was found to be maintainable over several thousandhours of operation with no detectable decay in cell performance.

As a further example, such catalytic structures for electrode use havealso been prepared without the step of converting the complex platinumsulfite acid to the sol. Specifically, the acid was adsorbed on thecarbon substrate, decomposed with air, and reduced with hydrogen. Duringsuch reduction, it was observed that H₂ S evolved, indicating theretention of sulfide materials; but the H₂ reduction at 400° C. wasfound to remove substantially all sulfides. Again particles in the20-Angstrom range were produced with similar electrode performance tothat above-presented.

A still additional example is concerned with deposition or adhering to arefractory non-conductive substrate of alumina. Sufficient complexplatinum sulfite acid to contain 200 milligrams of platinum was appliedto 50 cc. of insulative eta-alumina pellets, about 1/8 inch by 1/8 inch.The mixture was dried at 200° C. and, to effect decomposition andadsorption, was held at 600° C. in air for about 15 minutes. Thisresulted in a very uniform distribution of fine platinum particles(approximately 20 Angstroms) throughout the alumina surface structure,but not within the same. This was reduced by H₂ at 500° C. for abouthalf an hour, providing a significantly improved oxidation catalysthaving the following properties, considerably improved from HoudryPlatinum-on-Alumina Catalyst Series A, Grade 200 SR, a typical presentday commercial product, under exactly comparable conditions:

    ______________________________________                                        Ignition Temperature For                                                                         Invention  Houdry                                          ______________________________________                                        1. Methane         355° C.                                                                           445° C.                                  2. Ethanol         85° C.                                                                            125° C.                                  3. Hexane          145° C.                                                                           185° C.                                  ______________________________________                                    

Another example, again bearing upon this oxidation catalyst application,involves the same preparation as in the immediately previous example,but with two and a half times the amount of particulated platinum (i.e.500 milligrams). The following results were obtained:

    ______________________________________                                        Ignition Temperature For                                                                        Invention                                                   ______________________________________                                        1. Methane        340° C.                                              2. Ethanol        30° C. (room temperature)                            3. Hexane         130° C.                                              ______________________________________                                    

Still another example, identical to the previous one, but with 2 gramsof platinum adhered to the 50 cc alumina, was found to produce thefollowing results:

    ______________________________________                                        Ignition Temperature For                                                                        Invention                                                   ______________________________________                                        1. Methane        250° C.                                              2. Ethanol        30° C. (room temperature)                            3. Hexane         90° C.                                               ______________________________________                                    

Still another example, 200 milligrams of the preformed sol was adsorbedon alumina, and reduced with H₂ and found to produce the followingresults:

    ______________________________________                                        Ignition Temperature For                                                                              Invention                                             ______________________________________                                        1. Methane              310° C.                                        2. Ethanol              45° C.                                         3. Hexane               110° C.                                        ______________________________________                                    

For the usage of the last four examples, a range of platinum of fromabout 0.01% to 5% may be most useful, depending upon the economics andapplication.

As still a further example, the deposition of adsorption described inthe last four examples, above, may also be effected on other refractoryoxides in similar fashion, including silica and zirconia.

Lastly, other refractories, such as zeolites, calcium phosphate andbarium sulfate, may be similarly coated by the processes of the lastfour examples.

While the novel complex platinum compounds, acid and/or sol may beprepared by the preferred method previously described, it has been foundthat the acid may also be prepared from hydroxyplatinic acid (H₂Pt(OH)₆) by dissolving the same could is about 6% aqueous H₂ SO₃, andevaporating to boil off excess SO₂. This appears to yield the complexplatinum sulfite acid material, also (identified by its characteristictitration curve). While this process involves a lower pH, it should benoted that chloride is excluded by the starting material.

The above-described methods for the preparation of several platinumcompounds of unexpected utility as sources of superior catalysts forfuel cells, oxidation catalysts, etc. have proven quite satisfactory;specifically, for producing (I) the water-insoluble salt characterizedto have the composition of Na₆ Pt (SO₃ (₄ ; (II) the complexsulfite-platinum compound, soluble in water, and having an empiricalformula and composition represented substantially by H₃ Pt (SO₃)₂ OH;and (III) the colloidal dispersion or sol of a platinum compound ofunknown composition, but formed by the oxidative, thermal decompositionof (II).

Among the important before-described uses for these compounds is thepreparing of fuel cell catalysts, consisting of platinum supported oncarbon, having superior electrocatalytic properties.

Subsequent work has revealed new, unexpected and simplified means andsteps of preparing such superior forms of fuel cell catalysts. The basisfor all of the syntheses of a carbon-supported platinum fuel cellcatalyst is the formation of a platinum colloid, capable of beingdeposited on carbon to yield platinum supported on carbon of averageparticles size range of substantially of the order of 15-25 Angstroms,either as a colloid, as before described, which can be subsequentlycontacted with finely divided carbon, or as hereinafter described, ascolloid generated in the presence of such carbon, thereby causing thecolloidal platinum particles to be formed and deposited on the carbon ina single step. We will now describe in detail one especiallyadvantageous technique which involves, typically, the step of oxidizingthe sulfite ligand of the preferred complex platinum compounds (I) and(II) to sulfate, in aqueous solution, by means of a non-complexingoxidant, it being understood that other platinum complexes containingligands capable of being oxidized to substantially non-complexingproducts are also suitable, as later discussed.

Techniques for preparing a fuel cell catalyst, equivalent to that foundfrom the complexes (I) or (II), have been discovered, whereinchloroplatinic acid (CPA) and sulfite are reacted, to yield (II), butwherein, unlike the before-described methods, the complex acid (II) isnever separately isolated, but is converted to a catalyst directly, andwithout isolation from by-products, such as NCl and NaCl.

An illustration of the synthesis of a carbon-supported platinum fuelcell catalyst is the observation of the oxidizing reaction of thecomplex platinum sulfite acid (II) with H₂ O₂. When H₂ O₂ is added to adilute solution of the complex acid (II), the sulfite present in thesulfite-platinum complex, is oxidized. The solution's color slowlychanges from a faint yellow, to orange. Following the appearance of theorange color, a faint Tyndale effect is noted. With time, this becomesmore pronounced; the solution becomes cloudy, and finally, precipitationoccurs. While the material precipitated is of unknown exact composition,it is believed to be a hydrated oxide of platinum, since it is solublein base much as is hydrated platinum hydroxide or platinic acid, H₂ Pt(OH)₆. In any case, treatment of the complex platinum sulfite acid (II)with H₂ O₂ yields a meta-stable colloid of a platinum compound. Thesequence of reactions described above are hastened with heat, andproceed more slowly with increasing acidity, as from the addition ofsulfuric acid.

Whereas in the earlier-described methods, the platinum colloidal sol isfirst formed and then applied to the carbon particle substrate, if thereaction described immediately above is performed in the presence of thehigh surface area carbon, the carbon particles act both as nuclei and asa support for the extremely small particles of the platinum compound, asthey are formed, and they are deposited on the carbon rather thancoalescing to yield a lower surface area precipitate. It has been foundthat this carbon nucleation of the platinum particles permits therestriction of the platinum deposits to particular catalytic particlesof the said preferred 15-25 Angstrom size range.

It has also been found that the same reaction occurs if the complexsodium platinum sulfite precipitate (I) is acidulated by dissolving indilute sulfuric acid, and is then oxidized by treatment with H₂ O₂ ; orif CPA is reacted with NaHSO₃ or H₂ SO₃, to yield a sulfite-platinumcomplex, and then oxidizingly treated with H₂ O₂.

Several examples of the use of the reactions observed above are givenbelow. Basically, however, they all depend upon the oxidation of thesulfite present in a platinum-sulfite complex, with H₂ O₂ being thepreferred oxidant, although other non-complexing oxidants, such aspotassium permanganate, persulfuric acid and the like have been used.The term "non-complexing oxidant", as used in this specification and inappended claims, means an oxidant which does not introduce groupscapable of forming strong complexing ligands with platinum. Also whileany high surface area carbon is suitable, the carbon black, Vulcan XC-72(Cabot Corp.), has been found to yield an excellent catalyst; but thefact that this carbon is used in the examples to be cited does not implythat other carbons cannot be used. Nor, since the carbon is merely asupport onto which to deposit the colloidal particles of platinum asthey are formed, should it be thought that carbon is the only supportupon which the deposit can be made. Other materials such as Al₂ O₃,BaSO₄, SiO₃, etc. can be used as supports for a high surface areaplatinum, as previously described, but are, of course, useful for othercatalytic properties rather than for fuel cells, electrodes and thelike, because of their high electrical resistance. We shall now proceedto a further series of examples.

EXAMPLE 1

To a liter of water, sufficient of complex platinum sulfite acid (II) isadded to give a platinum concentration of 2.5 g/l. To this solution isadded 22.5 grams of Vulcan XC-72. The solution has an initial pH ofabout 1.8 which is unaltered by the addition of carbon. The solution isstirred vigorously, so as to keep the carbon well dispersed. Add 50 mlof 30% H₂ O₂, while continuing the vigorous stirring. Maintain thestirring for about one hour. The pH will drop slowly, indicating thathydrogen ions are being generated. Next, heat the solution to boiling,while maintaining the stirring. Filter the carbon, wash it well withwater, and dry the carbon in an over set to 100°-140° C. This air-driedmaterial is now ready for use without further treatment. Platinum uptakeis about 98% with the remainder being discharged to the filtrate. Theresulting carbon, containing 9.9-9.85 platinum shows platinumcrystallites of 5-20 Angstroms in diameter by electron microscopy. Fuelcell performance was measured using Teflon bonded anodes and cathodeshaving platinum loadings of 0.25 mg/cm² of electrode area. Performancewith H₂ and air, at 190° C. in a phosphoric acid fuel cell, was measuredand found to give 200 Amperes per square foot (ASF) at 0.670-0.680 V.The resistance loss was about 0.02 volts at this current density, so theIR-free performance was about 0.700 Volts as 200 ASF.

EXAMPLE 2

The reaction was conducted as in Example 1, but rather than heating thesolution after 1 hour, stirring was continued for 24 hours at ambienttemperature. Platinum uptake was 97-98%, and physical andelectrochemical properties substantially identical to the producedescribed in Example 1 were obtained.

EXAMPLE 3

The reaction of the complex platinum sulfite acid (II) with H₂ O₂ wasconducted much as in Example 1, except the pH of the solution wasadjusted to 3 with NaOH, prior to the addition of H₂ O₂. After the 1hour reaction period, the pH was again brought to 3 with NaOH, and thesolution boiled. Th carbon was filtered, washed, and dried, aspreviously described. Platinum uptake was substantially quantitative,and the physical and electrochemical properties of the productsubstantially identical to those described in Examples 1 and 2.

EXAMPLE 4

In 100 ml of H₂ O, sufficient of the complex sodium platinum sulfitesalt (I) was dissolved to yield a platinum concentration of 25 g/l. Thesalt was put in solution by the addition of sufficient H₂ SO₄ to dropthe pH to 2. This solution was diluted with H₂ O to volume of one liter,and reacted as described in Example 3. Platinum uptake was quantitativeand the physical and electrochemical properties of the productsubstantially identical to those already described in the previousexamples.

Before proceeding to Example 5, which describes a process that does notrequire the isolation of either of the complexes (I) or (II) but ratheruses CPA heated with sulfite, it maybe useful to hypothesize upon themechanism of the reactions taking place in Examples 1-4, since they havea bearing on the reaction of Example 5, and will help to explain some ofthe difficulties of control noted in Example 5; though the invention isnot dependent upon the accuracy of such hypothesis, it being sufficientto describe the steps that do indeed work and produce the results of theinvention.

It is believed, however that when H₂ O₂ is added to either the sodiumplatinum sulfite complex (I) or the like, dissolved in dilute H₂ SO₄, orto a solution of the platinum sol (III), the sulfite or like ligand isdestroyed. Since it is the complexing power of sulfite which is thestabilizing force in maintaining an ionic platinum species, itsoxidation to sulfate destroys this stabilizing force. Sulfate is, atbest, a feeble complexing agent for platinum, whether it is Pt^(II) orPt^(IV). With the removal of the sulfite, there does not exist afavorable environment for maintaining a soluble species of platinum, andthe platinum species just formed upon the destruction of the stabilizingsulfite must slowly hydrolize and in the process has a transientexistence as extremely small colloidal particles. It is these particleswhich are deposited on the carbon yielding the active catalyticstructure. It is believed that the reactions of Examples 1-3 can beadequately described as being substantially:

    H.sub.3 Pt(SO.sub.3).sub.2 OH+3H.sub.2 O.sub.2 -2H.sub.2 SO.sub.4 +PtO.sub.2 +3H.sub.2 O                                    (1) and (2)

    (3)Na.sub.2 HPt(SO.sub.3).sub.2 OH+3H.sub.2 O.sub.2 -Na.sub.2 SO.sub.4 +PtO.sub.2 +3H.sub.2 O+H.sub.2 SO.sub.4                   (3)

Example 4 is somewhat different, in that the starting material isdifferent. However, it would appear that when the complex salt ofcomposition Na₆ Pt (SO₃)₄ is dissolved in H₂ SO₄, the complex acid ofcomposition H₃ Pt (SO₃)₂ OH is formed, since there is a vigorousevolution of So₂, and when the SO₂ is evolved, the characteristictitration curve of H₃ Pt (SO₃)₂ OH is observed. Hence, the reaction ofExample 4 is apparently similar to that of Example 3.

In Example 5 presented below, however, CPA is reacted with NaHSO₃ toyield a complex believed to be the complex acid of composition H₃Pt(SO₃)₂ OH, and HCl and NaCl are formed. One possible reaction issubstantially as follows:

    H.sub.2 PtCl.sub.6 +3NaHSO.sub.3 +2H.sub.2 O-H.sub.3 Pt(SO.sub.3).sub.2 OH+Na.sub.3 SO.sub.4 +NaCl+5HCl

However, when this mixture is treated with H₂ O₂, the presence ofchloride, along with the high acidity, leads to the formation in part,of H₂ PtCl₆, rather than the desired colloidal species. To minimize thiseffect, the platinum concentration must be kept low (in order to keepthe chloride concentration low) and the pH closely controlled.

EXAMPLE 5

Dissolve 1 gram of CPA (0.4 gm Pt) in 100 ml water. Add 2 grams ofNaHSO₃ and heat until the solution turns colorless. Dilute to 1 literwith water and adjust the pH to 5 with NaOH. Add 3.6 grams of VulcanXC-72, and while stirring add 50 ml of 30% H₂ O₂. Continue to stir andas the pH changes, add NaOH to maintain the pH between 4 and 5. When thepH has stabilized, heat the solution to boil, and filter and wash thecarbon. Platinum pickup is variable, but in general is about 90%.Increasing the platinum concentration decreases the percentage ofplatinum deposited upon the carbon since the conversion of H₂ PtCl₆ isfavored. The catalyst formed in this way, has been found to besubstantially identical in performance to that made in Examples 1-4.

As compared with the earlier described methods of said priorapplications, also embodied herein, the additional methods, supra, avoidthe conversion of the compound having the composition of Na₆ Pt(SO₃)₄ tothat of composition H₃ Pt(SO₃)₂ OH, and then to the colloidal solmaterial. This latter colloid, in turn, must then be applied to carbon,filtered, dried, and reduced in H₂, in accordance with the earliermethods. As described in Example 4, however, the compound of compositionNa₆ Pt(SO₃)₄ is dissolved in acid, reacted with H₂ O₂ in the presence ofcarbon, the product filtered, washed and dried and with no H₂ reductionnecessary, since the sintering temperature required to prepare theelectrodes is ample to decompose the adsorbed species to thecatalytically-active platinum particles.

EXAMPLE 6

5 g of the precipitate having the composition corresponding to Na₆Pt(SO₃)₄ is suspended in about 100 cc of water and reacted with a largeexcess of the ammonium form of Dowex 50 (a sulfonated copolymer ofstyrene and divinylbenzene) cation exchange resin in bead form until theprecipitate is dissolved. The pH of the resulting solution is about 4.After filtration, the solution is passed through a column of Dowex 50 inthe ammonium form until all of the sodium is removed. The resultingplatinum sulfite complex in solution is then oxidized with hydrogenperoxide in the presence of finely divided carbon, using the procedureof Example 1, yielding a nearly equivalent electro-catalyst.

Similar results are obtainable by first neutralizing to pH 9 a solutionof the complex compound corresponding to H₃ Pt(SO₃)₂ OH with aqueousammonia which neutralization requires almost five moles of NH₃ (insteadof only 3 moles in the case of neutralization by NaOH), then acidifyingthe solution to pH 3 with sulfuric acid, and oxidizing with H₂ O₂ in thepresence of carbon, again using the procedure of Example 1.

In both the earlier methods of the said applications and the additionalmethods supplementarily discussed herein, however, common over-all stepsare involved of forming the complex sodium platinum sulfite precipitatefrom CPA, acidifying the same and developing the complex platinumsulfite acid and oxidizing such into a platinum colloidal sol, which isapplied to the carbon particle substrate and reduced to form theconduction catalytic fuel cell or related electrode.

While the above examples relate to a complex platinum sulfite as thestarting material for an appropriate platinum colloid, other platinumcomplexes comprising oxidizable ligands can be similarly used, as beforestated, to produce suitable platinum colloids by means of anon-complexing oxidant, as illustrated in the next Example 7.

EXAMPLE 7

Four grams of platinic acid, H₂ Pt(OH)₆, were dissolved in 25milliliters of 1 molar NaOH. Six grams of sodium nitrite were dissolvedin this solution and then the mixture was diluted to a volume of 800milliliters with water. The pH was then reduced from about 11 to pH of 2with H₂ SO₄. During the process, a precipitate formed and re-dissolvedas the pH approached 2, thereby forming a platinum nitrite complex. Tothis solution, 18 grams of finely divided carbon (Vulcan XC-72) wereadded, and while vigorously stirring, 200 millileters of 3% H₂ O₂ wereadded. The pH dropped to 1.4 substantially instantaneously. Theresulting platinum-catalyzed carbon was filtered, washed and dried. Fuelcell performance for 0.25 milligram per square centimeter electrodes ofthis material in a phosphoric acid fuel cell at 190° C., was 640millivolts at 200 amperes per square foot, with hydrogen and air.

In this case, the lower performance of this platinum nitrite complex, ascompared with the platinum sulfite complex, appears attributable to thefact that the colloidal state is rapidly produced and persists only fora very short time, followed by precipitation; whereas in the case of theplatinum sulfite complex, the oxidation proceeds slowly and the colloidis stable over long periods of time.

As before explained, in general, suitable electrocatalysts are preparedby depositing platinum of the 15-25 Angstrom particle size on finelydivided conducting carbon. It as also been found possible to preparecolloidal solutions, though not quite so efficacious, by the use ofsolutions of non-complex platinum salts from which colloidal solutionscan be made, for example, by the use of an appropriate hydrolysistechnique, as illustrated by Examples 8 and 9.

EXAMPLE 8

Four grams of platinic acid, H₂ Pt(OH₆, were dissolved in 10 milliletersconcentrated NHO₃. This solution was slowly added to one liter of watercontaining 18 grams of finely divided carbon (Vulcan XC 72) whilevigorous stirring was maintained for one hour, and then th pH wasadjusted to 3 with NaOH, while continuing stirring. The dispersion wasthen boiled, while stirring. This colloid was thus produced byhydrolizing a non-complex platinum salt solution at the aboveappropriate pH. The resulting platinized carbon was filtered, washed anddried. Fuel cell electrodes were fabricated therefrom having a platinumloading of 0.25 milligrams per square centimeter and a phosphoric acidfuel cell constructed. Performance with hydrogen and air at 190° C. was600 millivolts at 200 amperes per square foot.

EXAMPLE 9

The experiment of Example 8 was repeated except 6 molar H₂ SO₄ wassubstituted for nitric acid, this time producing the colloid byhydrolyzing the non-complex platinum salt resulting from the H₂ SO₄reaction at the same pH of about 3. Fuel cell performance under similarconditions as in Example 8 was 667 millivolts at 200 amperes per squarefoot.

The platinized carbon electrodes produced with the non-complex platinumsols of Examples 8 and 9, while most useful for the purposes described,have given somewhat lower fuel cell voltages at the same currentdensities than electrodes made from the preferred platinum sulfitecomplex, before discussed, apparently because of the difficultiesinvolved in controlling the hydrolysis conditions required for thenon-complexing platinum salt processes.

As before stated, while only illustrative electrode and other catalyticuses have been described, the invention is clearly applicable to a widevariety of electrodes, oxidation, hydrogenation, de-hydrogenation,reforming, cracking, chemical reaction-aiding, contaminant burning andother uses, as well, further modifications will also occur to thoseskilled in this art and all such are considered to fall within thespirit and scope of the invention as defined in the appended claims.

What is claimed is:
 1. In a fuel cell.[.and the like.]., a catalyticelectrode comprising an electrically conductive high surface area.Iadd.carbon .Iaddend.substrate on which has been deposited platinumparticles of the order of substantially 15 to 25 Angstroms in particlesize and in which said particles are formed from .[.one of.]. anoxidative decomposition of a platinum .Iadd.sulfite .Iaddend.complexcomprising an oxidizable ligand.[., and hydrolysis of a non-complexplatinum salt solution.]..
 2. In a fuel cell .[.and the like.]., acatalytic electrode as claimed in .Iadd.claim .Iaddend.1 and in whichthe platinum loads the electrode surface in the range of fromsubstantially 0.04 milligrams/cm² to 0.5 milligrams/cm².
 3. In a fuelcell .[.and the like.]., a catalytic electrode comprising anelectrically-conducting high surface area carbon substrate on which hasbeen deposited substantially uniformly platinum particles having aparticle size substantially in the range of 15 to 25 Angstroms and beingformed from the oxidative decomposition of a platinum .Iadd.sulfite.Iaddend.complex comprising an oxidizable ligand. .[.4. In a fuel celland the like, a catalytic electrode as claimed as in claim 3 and inwhich said complex is selected from the group consisting of platinumsulfite and platinum nitrite complexes..].
 5. In a fuel cell .[.and thelike.]., a catalytic electrode as claimed in claim .[.4.]. .Iadd.3.Iaddend.and in which said particles are reduced subsequent to saidoxidative decomposition.
 6. In a fuel cell .[.and the like.]., acatalytic electrode as claimed in claim .[.4.]. .Iadd.3 .Iaddend.and inwhich the platinum loads the electrode surface in the range of fromsubstantially 0.04 milligrams/cm² to 0.5 milligrams/cm².
 7. In a fuelcell .[.and the like.]., a catalytic electrode as claimed in claim.[.4.]. .Iadd.3 .Iaddend.and in which said platinum sulfite complex isthe compound having the composition corresponding substantially to H₃Pt(SO₃)₂ OH.
 8. A fuel cell comprising a catalytic electrode having anelectrically-conducting high surface area carbon substrate on which hasbeen deposited substantially uniformly platinum particles having aparticle size substantially in the range of 15 to 25 Angstroms andformed from the oxidative decomposition of a platinum .Iadd.sulfite.Iaddend.complex comprising an oxidizable ligand, .[.said complex beingselected from the group consisting of platinum sulfite and platinumnitrite complexes.]. and said particles being reduced subsequent to saidoxidative decomposition, said fuel cell being a phosphoric acidelectrolyte fuel cell with air-hydrogen electrode supply means, and saidelectrode being provided with means for enabling the drawing of currentflowing through the cell.
 9. A fuel cell as claimed in claim 8 and inwhich said electrode is a catalytic anode, and in which saidair-hydrogen electrode supply means comprise a source of hydrogencontaining carbon monoxide impurity.
 10. A fuel cell as claimed in claim9 wherein said catalytic anode has a platinum loading in the range offrom substantially 0.04 milligrams/cm² to 0.25 milligrams/cm².
 11. Afuel cell as claimed in claim 8 and in which the said carbon iscomposited with fluorinated hydrocarbon polymer.
 12. In the method ofpreparing electrodes for fuel cells .[.and the like.]. comprisingplatinum-on-carbon electro-catalyst, the steps of providing aqueouscolloidal platinum-containing sol having an average platinum particlesize substantially of the order of 15-25 Angstroms, depositing saidplatinum contained in said sol on an electrically-conducting carbonsubstrate, and controlling the depositing to cause the carbon tonucleate the deposit and limit the formation of platinum particles onsaid carbon to said size. In a fuel cell .[.and the like.]., anelectrode comprising a platinum-on-carbon electrocatalyst, saidelectrode being produced by a process including the steps of oxidizingthe ligand of a complex platinum .Iadd.sulfite .Iaddend.compoundcomprising an oxidizable ligand to substantially non-complexing productsby means of a non-complexing oxidant, producing therefrom an aqueousdispersion comprising the products of said oxidation, depositing theplatinum compound contained in said dispersion on an electricallyconducting carbon substrate, and decomposing said platinum compoundthereon, thereby forming platinum particles on said carbon having anaverage particle size of the order of substantially 15-25 Angstroms. 14.In a fuel cell .[.and the like.]., an electrode .[.produced by theprocess of.]. .Iadd.as claimed in .Iaddend.claim 13 wherein said complexplatinum compound is .[.platinum sulfite and it is.]. subjected to airoxidation.
 15. In a fuel cell .[.and the like.]., an electrode.[.produced by the process of.]. .Iadd.as claimed in .Iaddend.claim 14wherein said complex platinum sulfite .Iadd.compounds .Iaddend.containsgroups of (OH) and H₃ Pt(SO₃)₂.
 16. In a fuel cell .[.and the like.].,an electrode .[.produced by the process of.]. .Iadd.as claimed in.Iaddend.claim 14 wherein said air oxidation is carried out at about135° C.
 17. In a fuel cell .[.and the like.]., an electrode .[.producedby the process of.]. .Iadd.as claimed in .Iaddend.claim 13 wherein saiddispersion contains the product of said complex platinum sulfite and anon-complexing oxidant, said oxidation being carried out in saiddispersion.
 18. In a fuel cell .[.and the like.]., an electrode.[.produced by the process of.]. .Iadd.as claimed in .Iaddend.claim 17wherein said oxidant is selected from the group consisting of hydrogenperoxide, potassium permanganate and persulfuric acid.
 19. In a fuelcell .[.and the like.]., an electrode .[.produced by the process of.]..Iadd.as claimed in .Iaddend.claim 17 wherein said complex platinumsulfite is selected from the group of compounds having substantially thecomposition of Na₆ Pt(SO₃)₄ and H₃ Pt(SO₃)₂ OH and mixtures thereof. 20.In a fuel cell .[.and the like.]., an electrode .[.produced by theprocess of.]. .Iadd.as claimed in .Iaddend.claim 17 wherein said complexplatinum sulfite is the compound having the composition of Na₆ Pt(SO₃)₄and wherein said compound is in an aqueous sulfuric acid solution. 21.In a fuel cell .[.and the like.]., an electrode .[.produced by theprocess of.]. .Iadd.as claimed in .Iaddend.claim 19 wherein saidoxidation is effected with H₂ H₂.
 2. In a fuel cell .[.and the like.].,an electrode .[.produced by the process of.]. .Iadd.as claimed in.Iaddend.claim 13 wherein said oxidation is carried out in the presenceof said carbon substrate in finely divided form.
 23. In a fuel cell.[.and the like.]., an electrode .[.produced by the process of.]..Iadd.as claimed in .Iaddend.claim 13 wherein said complex platinumcompound is formed in said dispersion by reacting a solution ofchloroplatinic acid .[.and the like.]. with a sulfiting agent.
 4. In afuel cell .[.and the like.]., an electrode .[.produced by the processof.]. .Iadd.as claimed in .Iaddend.claim 23 wherein aid oxidation iseffected thermally in air, and said decomposing following depositing onthe carbon is effected by reducing the same.
 25. In a fuel cell .[.andthe like.]., a catalytic electrode comprising an electrically conductivehigh surface area carbon substrate on which has been deposited platinumparticles of the order of substantially 15 to 25 Angstroms in particlesize and in which said platinum loads the electrode surface in the rangeof from substantially 0.04 milligrams/cm² to 0.5 milligrams/cm².
 6. Afuel cell comprising a catalytic cathode electrode having anelectrically conductive high surface area carbon substrate on which hasbeen deposited platinum particles substantially of the order of 15 to 25Angstroms in particle size, said electrode having an electrode surfaceplatinum loading within the range of from substantially 0.04milligrams/cm² to 0.5 milligrams/cm², said fuel cell being anair-hydrogen high temperature fuel cell with a phosphoric acidelectrolyte and being capable of producing in excess of 100 Amperes persquare foot of electrode area at a cell voltage of at least 0.5 volts.27. A fuel cell as claimed in claim 26 and in which the platinizedcarbon is admixed with a fluorinated hydrocarbon polymer.
 28. A fuelcell comprising a catalytic anode electrode having an electricallyconductive high surface area carbon substrate on which has ben depositedplatinum particles substantially of the order of 15 to 25 Angstroms inparticle size, said electrode having an electrode surface platinumloading within the range of from substantially 0.04 milligrams/cm² to0.5 milligrams/cm², said fuel cell being an air-hydrogen hightemperature fuel cell with a phosphoric acid electrolyte, said hydrogencomprising carbon monoxide impurity, and said fuel cell being capable ofproducing in excess of 100 Amperes per square foot of electrode area ata cell voltage of at least 0.5 volts.
 29. A fuel cell as claimed inclaim 28 and in which the platinized carbon is admixed with afluorinated hydrocarbon polymer.
 30. A fuel cell as claimed in claim 28,and in which said fuel cell comprises a catalytic cathode having anelectrically conductive high surface area carbon substrate on whichsubstrate has been deposited platinum particles substantially of theorder of 15 to 25 Angstroms in particle size, the platinum loading ofthe cathode surface being within the range of from substantially 0.04milligrams/cm² to 0.5 milligrams/cm², said fuel cell having connectedthereto fuel and oxidant supply means and means for enabling drawingcurrent through the cell.
 31. A fuel cell as claimed in claim 26 and inwhich means is provided for operating said cathode electrode at atemperature of from substantially 135° to substantially 190° C.
 32. Afuel cell as claimed in claim 28 and in which means is provided foroperating said anode electrode at a temperature of from substantially170° to substantially 190° C.
 33. A fuel cell comprising a catalyticelectrode having an electrically conductive high surface area carbonsubstrate on which has been deposited platinum particles of the order ofsubstantially 15 to 25 Angstroms in particle size and formed from acomplex platinum sulfite .[.selected from the group of compounds.].having substantially the composition of Na₆ (Pt(SO₃)₄ .[.and H₃ Pt(SO₃)₂OH and mixtures thereof,.]..Iadd..
 34. A fuel cell as claimed in claim33 and in which said fuel cell comprises an additional electrode, anelectrolyte, fuel and oxidant supply means, and means for enabling thedrawing of current flowing through the cell. .Iadd.
 5. A fuel cellcomprising a catalytic electrode having an electrically conductive highsurface area carbon substrate on which has been deposited platinumparticles of the order of substantially 15 to 25 Angstroms in particlesize, with the average particle size being in that range, and formedfrom a complex platinum sulfite having substantially the composition ofH₃ Pt(SO₃)₂ OH. .Iaddend. .Iadd.36. A fuel cell as claimed in claim 35and in which said fuel cell comprises an additional electrode, anelectrolyte, fuel and oxidant supply means, and means for enabling thedrawing of current flowing through the cell. .Iaddend. .Iadd.37. Acatalyst electrode in accordance with claim 25, wherein the platinumparticles are adsorbed on the inherently porous carbon substrate..Iaddend. .Iadd.38. A catalytic electrode in accordance with claim 25,wherein the substrate comprises carbon black. .Iaddend. .Iadd.39. Acatalytic electrode in accordance with claim 38, wherein the platinumparticles are adsorbed on the carbon black. .Iaddend.